1. Field of the Invention
The present invention relates to a machine for applying a coating medium to a moving surface (e.g., a fiber material web, applicator roll or backing roll), and, more particularly, to a machine for applying a coating mixture to a moving surface using a coater rod.
2. Description of the Related Art
A machine for applying a liquid or viscid medium (such as sizing) to a moving surface may include a coater rod which is positioned closely adjacent to the moving surface. The distance between the coater rod and the moving surface during operation determines the thickness of the coating which is applied to the moving surface. Typically, the coater rod is connected to a beam or mounting via a coater rod bed and a blade. The blade is flexible and allows the coater rod to be moved toward and away from the moving surface using known adjustment devices, such as profile adjusting screws and a load tube. The coater rod bed is conventionally manufactured from a polyurethane material, such as those having a polyether or polyester base. Such materials include the physical property of being relatively resilient. The coater rod bed can therefore be constructed to clampingly engage each of the blade and the coater rod.
A problem with a conventional coater rod bed constructed of polyurethane is that such a material deteriorates when exposed to the operating environment of a coating machine. More particularly, polyurethane is susceptible to flaking and other permanent deterioration upon exposure to water, NaOH, and other solvents. A coater rod bed constructed of polyurethane must therefore be replaced from time-to-time because of such physical or chemical deterioration.
Another problem associated with using a coater rod bed constructed of polyurethane is that such a material is susceptible to swelling in the operating environment of a coating machine. The term "swelling", as used in this application, refers to chemically induced swelling of the coater rod bed caused by the exposure in the operating environment of the coating machine. The coater rod bed does not quickly return to its normal state upon occurrence of such chemically induced swelling. Such swelling may cause the coater rod bed to go out of dimensional tolerances, and further may result in an excessive, binding fit between the coater rod bed and the blade and/or coater rod.
Yet another problem with using a coater rod bed constructed of polyurethane is that such a material may not be capable of supporting a larger diameter coater rod during use. That is, a larger diameter coating rod has a correspondingly heavier weight which must be supported by the coater rod bed. A large diameter coater rod may exert sufficient loading on a polyurethane coater rod bed caused by gravitational force to physically deform the lip of the coater rod bed, which in turn may allow the coater rod to disengage from the coater rod bed. Alternatively, the heavy weight of a larger diameter coater rod may cause accelerated wear to the coater rod bed, which in turn results in more frequent and thus more costly repair and/or replacement.
What is needed in the art is a coating machine having a coater rod bed which is not susceptible to undue physical deformation and/or wear when carrying a larger diameter and thus heavier coater rod.